If it were in my diesel tank where I know storage conditions, I'd have no problem with 3 - 4 years. Right now I have 2 year old fuel in one tank which works*just fine.

If it were fuel that was suspect and stored for more than 2 years I'd pull a sample and let it sit for a day or two to see what settles out. But, how do you know that it is good stuff for your motor- take it to a testing lab. If in an old woodie and the tanks have gotten rusty and wet, I'd "trash" (give it*away)*the fuel and the tanks and start over.

the fuel has been on board in almost full tanks its at least 5 years old maybe older and there over 1000 gallons and fuel price are risinig fast than gold. my idea is filter it going off mix it with something like kerosine and some fuel additive . or add more #1 diesel to it . need some good ideas.

Every year I use about 50% of the total capacity of my tanks and add that back in, so some of the fuel in my tanks is from last yr, some from the yr before, some from the yr before that...........
The engines haven't revolted yet. the Racor 500 gets the big chunks (10microns) and the fiters on the engines get the rest (2 microns). When that stops working for me I'll start to worry about the age of my fuel. Until then.........

1,500 gallons of five year fuel was my max, but after polishing it through 30 microns, transferring it at 10 microns and pre-filtering at 2 microns I can't say I noticed any difference in my 3306 turbo.*

I was think after the first filter off the boat put in a booster, and something that well kill bacteria or what ever you call it. and then clean the tanks maybe steam them out and then flush them with some fuel and then put it back on with 2 micron and then use it.

and does ff have 3306 turbo's to***** still don't know what ff stands for does anybody else know.

If one believes lubricity additives*have a shelf life and cetane diminishes over time, there is more to using old dirty fuel than merely filtering it and adding mouse milk (attribute to RickB). Me, I'd include in the arsenal of use weapons a diesel testing lab - it is cheap insurance. Testing would throw out the suspicion that a derelict boat's tanks became an old oil, gas, diesel and cooolant dumping ground for others ( yup, it happens). What do your tanks tops look like?